Color change of the hottest screen printing

2022-07-25
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The change of silk printing color

this is a basic article written for inexperienced beginners, but the content contains an important enlightenment, that is, in the existing environment of printing plants, in order to obtain stable and high-quality prints, standards must be established

the most difficult is often to answer questions that seem simple. Some beginners often ask, why does the color change when printing? Why is it so difficult for the printer to keep the color of one movable part exactly the same as that of another movable part? It is so difficult for the designer of Zhongchuang experimental machine manufacturer to make special design according to the situation? The only answer is to adopt serious process control and automatic adjustment technology to minimize the change of color. This is an appropriate answer when you are just beginning to engage in silk printing and know nothing about the process. However, from the point of view of an experienced production printer, they do not necessarily understand a series of reasons for color changes

if simple line moving parts are printed, this is monochrome printing. At this time, four-color eye tone can be ignored. This answer is reasonable within a certain range. Specifically, the main factors to be considered are as follows

poor ink blending

if the pigments in the ink are properly blended, the common cause of color change is the added solvent. In a well controlled workshop, the ink should be supplied to the printing press at any time after it is ready, that is, the printing workers should not mix the ink. In many companies, the ink is not supplied to the printing press after being adjusted, but left to the printing workers to adjust. They add and mix the ink according to their own feelings. As a result, the pigment balance in the ink is broken. For water-based common ink or UV ink, the water in the ink acts in the same way as the solvent in the solvent ink. Adding water will make the dry ink film thinner, affect the color of the ink, and then reduce the color density. The causes of such problems can be further traced. In the ink warehouse, the ink dispensing workers do not use the weighing device, but only rely on their own judgment to add an appropriate amount of solvent, or mix improperly at the beginning, or change the mixing amount of ink during printing, so that the mixed ink will produce different colors. When this living piece is printed again later, this situation will become worse. Unless there is enough ink matching records, it is almost impossible to reproduce a color

inappropriate selection of silk

any silk printer will encounter trouble if he thinks that the number of silk meshes is only a variable of silk structure, which will only affect the deposition of printing ink. The wire diameter and weaving method, i.e. plain or twill, have a great influence on the thickness of the printed ink film. The silk supplier will provide detailed technical data of silk, among which the most important theoretical ink volume, which represents the amount of ink passing through the silk hole under certain printing conditions, is generally expressed in cm3/m2. For example, a 150 mesh/cm wire with a wire diameter of 31 μ m. Will be able to pass 11cm3/m2 of ink. One wire diameter is 34 μ m. 150 mesh silk per square meter will pass 6cm3 of ink, equivalent to 11 and 6 μ M thick wet ink layer. It can be seen that the simple expression of 150 mesh will make you get significantly different ink layer thickness, and the result will cause great differences in color

with the improvement of silk weaving technology, it is possible to obtain a certain number of twill silk instead of plain silk. Although it is sometimes possible, it is very unlikely. Sometimes silk suppliers store some old twill silk. Generally speaking, the theoretical ink volume of these silk changes by 10%. If you use twill braided silk to print fine-grained images, there are more fine line breaks than plain silk

Tension of the

version

the lower tension of the version will cause the silk to separate from the printed surface slowly, which will affect the ink staying on the silk and cause uneven color and other effects. In this way, the color appears to have changed. To solve this problem, we must increase the distance between the horizontally placed silk plate and the substrate. Increasing the distance means to increase the pressure of the doctor blade. In this way, the amount of ink passing through the wire will be affected, resulting in further changes in color

setting of the doctor blade

we know more and more about how the doctor blade operates. Recent research shows that there are some interesting phenomena in the doctor blade during the printing operation, which will be described in detail later. Based on the current technical situation, the softer the doctor blade used to make the experimental data accurate and reliable, the more ink will pass through the silk. The greater the pressure acting on the doctor blade, the faster the blade of the doctor blade will wear during printing. This will change the contact point between the doctor blade and the printed matter, which will also change the amount of ink passing through the wire, thus causing color changes. Changing the scraping angle will also affect the ink adhesion. If the doctor blade runs too fast, this will reduce the thickness of the attached ink layer

setting of ink return blade

you will be surprised to find that many silk printers do not understand that the setting of ink return blade will have a significant impact on the adhesion of ink. The function of the ink returning knife is to fill the silk hole with a certain amount of stable ink. Adjusting the pressure, angle and sharpness of the ink returning knife will make the hole ink too much or too little. Too much pressure on the ink return knife will force the ink through the hole, resulting in too much ink adhesion. Insufficient pressure of the ink return knife will cause only part of the hole to be filled with ink, resulting in insufficient ink adhesion. The running speed of the ink return knife is also very important. If it runs too slowly, the ink will overflow; Running too fast will cause serious ink shortage, which is similar to the effect of changing the running speed of the scraper

machine setting

careful process control is the most critical factor. The stable and consistent adjustment of the machine means the stable and consistent color. If the machine adjustment changes indefinitely, the color will lose control. This problem usually occurs when the printing workers change shifts, or later printing workers change the printing machine at will to adapt to their own habits. The attention is not to touch the setting of the weight behind the oil source and the internal things, which will cause the color change. The latest multicolor printing press uses computer automatic control to eliminate this possibility. These stable and consistent settings shall be made to the printing machine, and these settings shall remain unchanged throughout the printing operation

influence of substrate materials

in the silk printing industry, the consistency of substrate materials to be printed is often neglected. The paper, paperboard and plastic used in printing are generally produced in batches. A high-quality supplier can guarantee that the whole batch of materials provided by it have good surface smoothness, but this is not always the case. During the processing of these materials, any small change in the process will change the color and surface finish of the materials. Once this happens, the color of the printing will appear to change, although nothing has changed in the actual printing process. When we want to print the same pattern on a variety of materials from corrugated plastic board to fine art cardboard as advertising, printers will encounter these practical difficulties. Another problem we often encounter is that our silk printing has to catch up with offset printing. If we do not pay attention to process control, we will have no chance. Careful process control includes accurate color measurement, line color measurement with spectrophotometer and three primary colors measurement with densitometer, so that we can print stable and consistent color images on various materials. If we still use the traditional intuitive method, the change of color may be so large that the process is completely out of control although the temperature remains the same

observe the light source

the color looks different under different light sources, and human eyes are very sensitive to these changes. This effect can be reduced by ensuring that the colors of the pigments used in the ink distribution throughout the printing operation are accurate and consistent. If the supplier is changed, it may be a disaster. The measurement and feeling of color is a very complex field. To achieve the best control, there must be a closed cycle composed of ink manufacturer, ink distribution, proofing and accurate measurement in the printing process

drying effect

sometimes the color changes due to improper adjustment of the dryer. When printing paper or paperboard, if the drying temperature is adjusted too high, the general situation is that white turns yellow. The glass and ceramic industries are most troubled by the color changes during drying or baking. The pigment used here should be completely changed from the printed color to the sintered color. The color of these sinters is affected not only by the baking temperature, but also by oxidation or the decline of air quality in the baking area

the above are just a few of the many reasons for color change, and also one aspect that makes silk printing so interesting and challenging. All these come down to one point, that is, good process control

· source: silk printing

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